1. Field of the Invention
The invention relates to a casing structure for a motor which may be used, for example, in electrical equipment of a vehicle.
2. Description of Related Art
Hitherto, a motor of the above-stated kind has had a casing the whole of which is made of iron, a ferromagnetic substance. This is because the casing is required to form a magnetic circuit in cooperation with a permanent magnet fixed to a cylindrical inner peripheral surface thereof. The use of iron, however, results in the motor per se being of a great weight, thereby presenting an obstacle to the achievement of reductions in the weight of motors, such reductions being demanded today. The casing made of iron is also disadvantageous in that it has such a poor heat dissipating ability that the motor may have an excessively high temperature when the motor is used in a high-temperature atmosphere, such as the inside of the engine room of a vehicle, or when the motor generates heat during operation thereof.
In order to reduce the weight of the motor, it is possible to form the casing from aluminum, a substance having a relatively small specific gravity. However, aluminum, which is a non-magnetic substance, accordingly, is not able to form a part of a magnetic circuit and, therefore, cannot be readily adopted.